D e p a r t m e n t o f A r c h I t e c t u r e _ U n I v e r s I t y o f T h e s s a l y _ G r e e c e Accessibility Instrument: connectivity (working

D e p a r t m e n t o f A r c h I t e c t u r e _ U n I v e r s I t y o f T h e s s a l y _ G r e e c e

Accessibility Instrument: connectivity (working title)

Measures: Metric Reach, Directional Reach

Instrument developed at Morphology Lab, College of Architecture, Georgia Tech, Atlanta, USA (2007-2011)

The instrument approaches accessibility through the notion of street connectivity. It has a twofold character METRIC and SYNTACTIC

Software: Spatialst_Lines (on a GIS platform)

Same theoretical context as space syntax


Accessibility Instrument: connectivity

Starting point:

Configurational approach of street networks enables us to have a generalized description of urban spatial structure without evoking information about land uses.

Why it is important?

Street networks enable cities to function and provide the physical framework for shared life. Street networks remain relatively stable over long periods of time , they act as the public constitutional framework that governs the redeployment of population and land uses on private properties.

How it can contribute to urban design?

From the point of view of the evolution of design of cities the fundamental question is: How does the configuration of streets and the density of streets and land division support the other kinds of densities which are characteristic of urbanism. Empirical Research has shown that connectivity of street networks is a factor that affects accessibility.



Measures: Metric Reach, Directional Reach

Concept and software developed at Morphology Lab, College of Architecture, Georgia Tech, Atlanta, USA (2007-2011)

Input data: street networks are represented in standard GIS format [ central lines, segments , nodes)

Software: Spatialst_Lines (on an Arcview platform which enables access to databases (land use distribution, population data, traffic volume, etc)



Metric reach is very similar to walking catchment areas.

It is a measure of the total street length accessible within a specific walking distance from the center of each street segment in an urban network

Parametric measure. Threshold (distance to be traveled)

A measure of density

Metric Reach, Directional ReachMeasures:



The mean metric reach is different than street length, number of intersections or number of blocks

1. Same street length

3. Same no of blocks and same no of intersections

2. Same street length and no of intersections

The question of configuration



Directional reach is a syntactic measure. It measures the total street length accessible within a specific number of direction changes from the center of each street segment in an urban network. A direction change is defined as a turn larger than a parametrically defined threshold.

Whereas metric reach extends uniformly along the streets surrounding a given street segment, directional reach may extend much less uniformly, because it is sensitive to the shape and alignment of streets, not merely to their density

Metric Reach, Directional ReachMeasures:



Metric Reach map of Atlanta Max distance ¼ mile

output



Directional Reach map of Atlanta2 changes of directionParametric threshold 10 degrees

output



Importance for planning and design practices

1. The measures of street connectivity are easy to implement on a GIS platform and results are easy to be related or tested against standard data.

2. They are able to provide criteria for the evaluation and development of designs and regulatory frameworks that support pedestrians’ accessibility and to differentiate between proposals that equally cover the quantitative demands of a design brief.



KAUST Science Town Masterplan, by Perkins + Will (2010)

D e pt. o f A r c h I t e c t u r e _ U n I v e r s I t y o f T h e s s a l y _ G r e e c e / assoc. , prof, Vaso Trova


References

2011, A. Ozbil, J. Peponis and B. Stone, Understanding the link between street connectivity, land use and pedestrian flows, Urban Design International 16, pp 125-141

2008, J. Peponis, S. Bafna, Z. Zhang, The connectivity of streets: Reach and Directiobal distance, Environment and Planning B: Planning and Design vol 35, pp 881-901

2007, J.Peponis, D. Allen, S. French, M. Scoppa, J. Brown, Street connectivity and urban density, Proceedings, 6th International Space Syntax Symposium, Istanbul

Documents

D e p a r t m e n t o f A r c h I t e c t u r e _ U n I v e r s I t y o f T h e s s a l y _ G r e e c e Accessibility Instrument: connectivity (working